1. Field of the Invention
The present invention relates to an apparatus and method for balancing a spin motor of a hard disk drive.
2. Description of Related Art
Hard disk drives contain a plurality of magnetic transducers that are coupled to a number of rotating disks. The transducers are typically incorporated into a slider that is supported by an actuator arm. The sliders each have an air bearing surface which creates an air bearing between the transducers and the rotating disks. The air bearings prevent mechanical wear of the transducers. The efficiency of reading and writing information onto the disk is a function of the air bearing height. It is desirable to maintain a constant air bearing height over the entire surface of the disk to prevent head contact and provide a consistent magnetic coupling efficiency.
The disks are typically rotated by a spin motor that is mounted to a base plate of the disk drive. Because of manufacturing tolerances the spin motor may be dynamically imbalanced after initial assembly. Any imbalance may introduce a wobble that will vary the air bearing height of the sliders. Disk drive manufacturers typically test and balance each spin motor at a test station before mounting the motor to the base plate of a drive.
For disk drives that contain multiple disks the spin motor is typically balanced in a first top plane and a second bottom plane. The motor is balanced by adding weights to various portions of the rotating motor hub. The top plane is typically balanced by set screws that are attached to the top of the hub. The bottom plane is typically balanced with a weight that is glued to a groove in the bottom portion of the hub.
Balancing and handling a multiple disk spin motor assembly in a test station separate from the disk drive introduces a process step that may damage the assembly. Additionally, gluing a weight to the hub assembly is undesirable because the adhesive may out-gas and contaminant the disks. The weight may also become detached from the hub and damage the drive. Furthermore, placing the weight in the bottom of the hub limits the diameter and the structural integrity of the motor spindle. It would be desirable to provide a method for balancing a spin motor while the motor is attached to the base plate of the disk drive.